This invention relates generally to shaft and nut assemblies, and, more particularly, this invention relates to a system for delashing a shaft and nut assembly.
One of the more common problems associated with shaft drive assemblies involves axial play or backlash between the bearings and shaft. This backlash, which is a function of the manufacturing tolerances associated with the drive assembly components, causes uneven wear, noise, and poor response when either the shaft or bearings begin traveling axially along the other. Examples of this type of assembly include worm/wormgear and ball-screw/ball-nut drives. In each case, a time varying axial load is exerted on a shaft, which may cause the previously noted problems in the presence of backlash in its mounting(s). Electric steering mechanisms, as many others, require shaft and ball bearing assemblies wherein the axial lash must be removed from the ball bearings without adding substantial friction to the assembly which would degrade the overall performance.
In some cases, such shaft/bearing assemblies employ springs bearing on the inner or outer races of the ball bearing assemblies, which, when preloaded, remove the axial lash. Such solutions, however, have relatively high compliance and are still prone to rattle under extreme vibratory duress or impact, and the manufacturer must recover the cost of the springs, the preparation of the mounting surfaces, etc. In other cases, simple nut tensioning devices are used, such that in tightening the nut onto the shaft or into the support housing, the inner or outer race of the ball bearing assembly may be slightly displaced, again removing the axial lash. These approaches are all too frequently difficult to control, as axial force is dependent on thread condition, cleanliness, fit, and other such concerns.
Pains have been taken in certain cases to tighten the nut portion of the assembly by some automated technique, tightening the shaft/nut interface while simultaneously measuring the assembly's resistance to rotation. This approach has the problem in that it is difficult to apply torque to the shaft without affecting the sensed reaction at the same time. Further, because the tightening mechanism remains coupled to some degree with the torque sensing device, the measurement of the shaft assembly's resistance to rotation is easily confounded.